Abstract

Laboratory measurements of air–water gas transfer rates for cleaned and film-covered water surfaces have shown that the presence of soluble and insoluble surfactants can inhibit air–water gas fluxes. Naturally occurring surface-active material is known to concentrate in the marine surface microlayer and form films and slicks. It is reasonable that oceanic slicks and films may lower in situ gas transfer rates compared with air–sea gas exchange through a clean ocean surface. Here, a simple model of gas transfer through clean and surfactant-influenced water surfaces is used to develop parameterizations of liquid-phase, and gas-phase, rate-controlled gas transfer velocities through clean and surfactant-influenced ocean surfaces. The parameterization for liquid-phase, rate-controlled processes is used to estimate the effect of naturally occurring surface films on the net global flux of carbon dioxide. The gas-phase, rate-controlled relations are used to study the impact of films on the flux of ammonia from the central Pacific Ocean.

By relating the fractional area coverage of surfactant-influenced sea surface to a global map of net synthetic primary production, the model shows that surface films can increase or decrease the net global oceanic carbon dioxide flux, depending on the regional film coverage.

Introduction

Motivation and purpose

There is little doubt that under laboratory conditions both soluble and insoluble surfactants suppress gas–liquid mass transfer rates.